This application claims the priority of Korean Patent Application No. 2003-3667, filed on Jan. 20, 2003, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.
1. Field of the Invention
The present invention relates to an optical switch using a micro-electromechanical system (MEMS), and more particularly, to a 2xc3x972 way optical switch.
2. Description of the Related Art
U.S. Pat. Nos. 6,303,885, 6,315,462, and 6,229,640 disclose techniques for a 2xc3x972 way optical switch used in various optical applications. Optical switches disclosed in U.S. Pat. Nos. 6,229,640 and 6,315,462 have a structure in which a mirror is driven by an electro-static comb drive and the optical switch disclosed in U.S. Pat. No. 6,303,885 has a structure in which a mirror is driven by spring arms. The structures of the optical switches have a common feature in that the mirror moves in parallel with the plane of a substrate by an actuator.
FIG. 1 is a microscopic photo of a conventional 2xc3x972 comb drive optical switch having two inputs and two outputs, and FIG. 2 is a plane view of a portion marked with dotted lines in FIG. 1 to explain the conventional 2xc3x972 comb drive optical switch shown in FIG. 1.
As shown in FIGS. 1 and 2, first and second optical input fibers 2a and 2b, and first and second optical output fibers 3a and 3b are arranged at around the central point P at an angle of 90 degrees. A mirror 1 is positioned at the central point P of the first and second optical input and output fibers 2a, 2b, 3a, and 3b. 
As shown in FIG. 3, when the mirror 1 is positioned out of the central point P, optical signals incident through the first and second input fibers 2a and 2b proceed toward the first and second output fibers 3a and 3b on the same axes with the first and second input fibers 2a and 2b without being reflected.
As can be seen in FIG. 4, when the mirror 1 is positioned at the central point P, an optical signal incident through the first input fiber 2a is reflected from one side of the mirror 1 and then proceeds toward the second output fiber 3b, and an optical signal incident through the second input fiber 2b is reflected from the other side of the mirror 1 and then proceeds toward the first output fiber 3a. 
Here, as shown in FIG. 4, when an optical signal is reflected by a mirror, the optical signal is reflected out of the central point of the mirror. Thus, the reflected optical signal does not proceed toward the central point of a target fiber. This is caused by an offset of an optical path due to the thickness of the mirror.
The offset causes light loss. The thicker the mirror, the greater the offset, which increases light loss. Accordingly, the thickness of the mirror is required to be reduced as it can be in order to reduce the offset of an optical path changed by the mirror. However, since in the above-described comb drive optical switch, the mirror moves in parallel with the plane of the substrate and a reflective surface of the mirror is perpendicular to the plane of the substrate, there is a limitation in reducing the thickness of the mirror. In particular, when forming a mirror, silicon is vertically etched in a plasma process, and then a metal having a high reflectance is deposited on the surface of the resultant structure. Thus, it is difficult to reduce the thickness of the mirror. Also, since the vertically etched surface is used as a reflective surface, a large amount of light is lost when light is reflected. Furthermore, since a high-priced silicon on insulator (SOI) wafer not a general wafer is used, cost for manufacturing the mirror is high.
The present invention provides an optical switch capable of reducing an offset of an optical path by reducing the thickness of a mirror.
The present invention also provides an optical switch which can cause a small amount of light loss and be manufactured at a low cost.
According to an aspect of the present invention, there is provided an optical switch including a substrate, a first input fiber and a first output fiber, a second input fiber and a second output fiber, a rotating mirror, torsion bars, and an electrostatic force generating part. The first input fiber and a first output fiber are arranged at a predetermined distance from a central point in a first optical path passing through the central point over the substrate. The second input fiber and a second output fiber are arranged at a predetermined distance from the central point in a second optical path that passes through the central point and is orthogonal to the first optical path. The rotating mirror is positioned at around the central point and turns on a turning shaft extending in parallel with the substrate. The torsion bars support the rotating mirror so that the rotating mirror rotates. The electrostatic force generating part supplies a drive force to the rotating mirror.
In an aspect of the invention, trenches into which the first and second input fibers and the first and second output fibers are inserted are formed in the substrate along the first and second optical paths.
In an exemplary embodiment of the invention, the rotating mirror has a first position where the rotating mirror is parallel with the substrate and a second position where the rotating mirror is perpendicular to the substrate, and turns from the first position to the second position by the electrostatic force generating part.